According to a typical railway vehicle, running (moving) of the vehicle is realized by a rotational force which is generated from a main motor (hereinafter abbreviated as a “motor”) attached to a truck disposed below a floor of the vehicle body, and transmitted to wheels of the truck via a joint (coupling) and a gear unit (gear box).
This type of motor in related art is chiefly constituted by an inductive motor which includes a cage rotor provided with a rotary iron core, a plurality of rotor bars embedded in the rotary iron core, and a short-circuit ring which connects extended portions of the respective rotor bars projected from the rotary iron core in the axial direction of a rotor shaft and combines the extended portions into one electrical body.
This inductive motor often has a so-called fully enclosed structure which separates the interior of the motor containing the rotor bars, coils constituting a stator, and other electrical parts from outside air. This structure adopts such a cooling system for a motor known in the art which achieves cooling not by introduction of the outside air into the motor but by airflow of the outside air, the flow caused by two fans rotating with the rotor shaft, without introducing the outside air into the electrically and magnetically cooperating motor components within the enclosure of the fully enclosed structure.
For example, an inductive motor in related art includes two fans: one positioned between an iron core supporting member for supporting the rotary iron core and one of a pair of bearings for supporting both ends of the rotor shaft in such a manner that the rotor shaft can freely rotate; and the other positioned between the iron core supporting member and the other bearing. Each of the fans includes a plurality of impellers provided almost radially on the surface of the fan facing to the outside in the axial direction. The outer circumferential edge of each of the fans is opposed to a housing separating the interior of the motor from the outside with an extremely small clearance between the edge of the fan and the housing, in which clearance a labyrinth seal structure is formed. According to the inductive motor thus constructed, the rotary area and the stationary area are partitioned, constituting the so-called fully enclosed structure as noted above where the interior components of the motor is separated from the outside air.
A part of each housing overlies, and thus covers, the fan in the axial direction. This part of the housing forms a shroud over the interior, fully sealed enclosure, portion of the motor, to form a cooling passage between the shroud and the sealed enclosure. An air inlet port is formed in a portion of the housing overlying the fan forming an inlet port positioned in the vicinity of the bearing on the driving side of the motor, to allow outside air to flow within the cooling passage past, and cool, the bearing and a side of the stator adjacent thereto. This air inlet port communicates, through an air channel formed within the housing, with an air channel which extends through a stator iron core of the stator in the axial direction, to cool the stator.
An air inlet port and an air outlet port are further formed in the housing covering the axial outside portion of the fan on the other bearing side. Again, a portion of the housing forms a shroud spaced from the sealed enclosure of the motor, to form a cooling passage/air channel therebetween. The inlet and outlet ports are formed as openings in the shroud located in the vicinity of the other bearing.
When the rotor shaft of the inductive motor thus constructed rotates, the fans rotate accordingly. As a result, outside air is introduced through the air inlet ports by a suction force generated by the impellers formed on the fans. Then, on the one bearing side, the outside air introduced via the air inlet port sequentially flows as cooling air through the air channel within the housing and the air channel within the stator iron core, and then exits through the outlet. During this process, cooling for the one bearing, cooling for the coils via the stator iron core, and cooling for the rotor bars via the fan, the iron core supporting member, and the rotor iron core can be simultaneously achieved.
On the other bearing side, the outside air introduced through the air inlet port flows toward the air outlet port as cooling air, and then goes out for discharge. During this process, cooling for the other bearing, and cooling for the rotor bars via the fan, the iron core supporting member, and the rotor iron core can be simultaneously achieved.
The structure which cools the respective components by using the fans discharges the outside air via the air channels or the air outlet port to the exterior of the housing after introducing and utilizing the outside air as cooling air, and therefore generates noise in the process. When the vehicle speed increases, the number of revolutions of the motor increases, in which condition noise generation easily occurs. Particularly, the air outlet port for the fan on the other bearing side located on the side opposite to the coupling in the axial direction is located in the vicinity of the corresponding fan, i.e., the impellers are directly exposed to the external environment through the exhaust port. In this case, the wind noise generated by the rotation of the impellers is emitted via the air outlet port to the outside in such a manner as to directly diffuse in a substantially sectored shape, in other words, along a cone shape formed at the edges of the line of sight to the impeller through the discharge opening. In contrast, the air exhaust from the driving side of the motor crosses the motor and exhaust at the non-driving side of the motor, remote from the fan. Accordingly, noise generation tends to easily increase when the fan rotates at a higher speed.
There are several methods considered as possible solutions to reduction of the noise generated from the fan disposed on the other bearing, non-driving, side, including a structure which decreases the opening area of the air outlet port, and a structure which positions the air outlet port away from the impellers so as to reduce the diffusion angle of the noise, for example. According to these methods, however, the amount of air flow is restricted and thus decreases, in which condition sufficient cooling effects are difficult to be provided.
Particularly, in the case of the structure which located the air outlet port away from the impellers, a guide is formed as a portion projecting in such a manner as to extend from the casing to the outside in the axial direction of the motor, for example. In this case, if the channel length of the cooling air becomes sufficiently long, and the air outlet port can be disposed away from the impellers. According to this structure, however, it is difficult to maintain the size of the envelope of the motor and housings to the size of the motor and housings established beforehand, i.e., the constrained space into which the motor and housing may be fitted in the trucks of the train.
In general, the motor attached to the truck has a severe size design limit determined beforehand, i.e., dictated by the available space in the truck, regardless of the type of motor.
More specifically, the motor is attached to the truck in such a condition that the axial direction of the rotor shaft is dictated by the lateral width direction of the vehicle. According to this structure, the motor is disposed in the space between the opposed wheels. In this case, at least a coupling and a gear box are also provided between the wheels and the motor. Accordingly, it is needed to position at least the motor, the coupling, and the gear box close to each other within the limited space between the wheels, imposing severe limitations on the size of the motor in the axial direction. In addition, the motor is attached between the cross beam of the truck and the axle in the front-rear direction of the vehicle. Thus, a severe limitation is also imposed on the size of the motor in the radial and width directions.
Accordingly, it is required to design the motor within the range of the severe limitations discussed above. Particularly, the size of the motor is an important factor which affects the output and performance of the motor, wherefore the motor needs to be designed based on sufficient experiences and various types of skills. In other words, it is essential to design the motor while utilizing technologies capable of securing the maximum output and performance, skills for improving the structure of the motor, and other techniques without exceeding the limited size.
However, when the guide extends from the casing as in the structure discussed above, the size increases by the amount of extension. In this case, it is difficult to size the motor within the predetermined size limitation or constraint and simultaneously extend the exhaust port away from the fan impellers to reduce noise.